(CBS/AP) FRENCH CAMP, Calif. - Two more possible victims of the "Speed Freak Killers" were identified Friday, more than 25 years after they disappeared from their Stockton homes, authorities said.

In total, the remains of four missing young women from the Central Valley have been found this year as a result of death row inmate Wesley Shermantine's crudely drawn maps directing authorities to burial sites.

In the latest discovery, San Joaquin County Sheriff Steve Moore said the remains of Kimberly Billy, who went missing in 1984 at the age of 19, and JoAnn Hobson, who disappeared in 1985 at 16, were among the hundreds of bone fragments found last month in an abandoned well near the farming town of Linden.

Authorities said they were working to identify the remains of a third body found in the well.

"At this point, of those 1,000 bone pieces that were recovered from the well, the forensic anthropologist has been able to reconstruct what they believe to be three individuals," Moore said.

Investigators believe they were victims of Shermantine and Loren Herzog, who authorities say went on a methamphetamine-fueled killing spree in the 1980s and 90s.

Searchers were directed to the well by Shermantine, who hand-drew maps in his San Quentin Prison cell after a Sacramento bounty hunter promised to pay him for information about victims.

Authorities also unearthed the remains of two other young women in February who were believed to be the victims of Shermantine and Herzog.

Shermantine is now on death row for four murders. Herzog hanged himself in January after the bounty hunter told him Shermantine was disclosing locations of victims.

Shermantine, who blames Herzog for the killing spree, told authorities that 10 or more bodies could have been stashed at the Linden well.

Before his suicide, Herzog maintained Shermantine was responsible for the deaths.